docs: def ensure_block_device(block_device):
      '''
      Confirm block_device, create as loopback if necessary.
  
      :param block_device: str: Full path of block device to ensure.
  
      :returns: str: Full path of ensured block device.
      '''
      _none = ['None', 'none', None]
      if (block_device in _none):
          error_out('prepare_storage(): Missing required input: block_device=%s.'
                    % block_device)
  
      if block_device.startswith('/dev/'):
          bdev = block_device
      elif block_device.startswith('/'):
          _bd = block_device.split('|')
          if len(_bd) == 2:
              bdev, size = _bd
          else:
              bdev = block_device
              size = DEFAULT_LOOPBACK_SIZE
          bdev = ensure_loopback_device(bdev, size)
      else:
          bdev = '/dev/%s' % block_device
  
      if not is_block_device(bdev):
          error_out('Failed to locate valid block device at %s' % bdev)
  
      return bdev